Convert any encoding to UTF 8 in Go

I'm downloading messages via IMAP. Next I'm adding parsed message into MongoDB. And I've a problem, because MongoDB support only UTF 8. And I wanna convert any encoding to UTF 8. Codes are various. How can I convert each string to UTF 8?

I know, that I can convert to binary, but I have to have normal text, because I have to searching phrases in database. Unless, can I searching normal text in binary?

I'm using the go-charset project to do this: https://code.google.com/p/go-charset/

It's pretty straightforward, you create a reader from a charset and it translates to utf-8 automatically. example from the library:

r, err := charset.NewReader(strings.NewReader("\xa35 for Pepp\xe9"), "latin1")
if err != nil {
    log.Fatal(err)
}
result, err := ioutil.ReadAll(r)
if err != nil {
    log.Fatal(err)
}
fmt.Printf("%s\n", result)  //outputs £5 for Peppé

Now, in my case I know the charset because it comes from web pages and I read the headers/meta tags. If you need to detect the charset automatically by heuristics, you'll need another library for that, such as this one: https://github.com/saintfish/chardet

I haven't used it but it also looks pretty simple to use:

detector := chardet.NewTextDetector()
result, err := detector.DetectBest(some_text)
if err == nil {
	fmt.Printf(
		"Detected charset is %s, language is %s",
		result.Charset,
		result.Language)
}

In 2020 I found that https://pkg.go.dev/mod/golang.org/x/text worked well for me.

package main

import (
	"bytes"
	"fmt"
	"io/ioutil"
	"log"

	"golang.org/x/text/encoding/ianaindex"
	"golang.org/x/text/transform"
)

func main() {
	text := "\xa35 for Pepp\xe9"
	charset := "latin1"
	e, err := ianaindex.MIME.Encoding(charset)
	if err != nil {
		log.Fatal(err)
	}
	r := transform.NewReader(bytes.NewBufferString(text), e.NewDecoder())
	result, err := ioutil.ReadAll(r)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("%s\n", result) //outputs £5 for Peppé
}

https://play.golang.org/p/Hl7r146UwhT

charset.NewReader in package golang.org/x/net/html/charset can't deal with encoding gb2312. charset.NewReaderLabel can deal with it.

import 	(
    "io/ioutil"
    "golang.org/x/net/html/charset"
)

func convrtToUTF8(str string, origEncoding string) string {
    strBytes := []byte(str)
    byteReader := bytes.NewReader(strBytes)
    reader, _ := charset.NewReaderLabel(origEncoding, byteReader)
    strBytes, _ = ioutil.ReadAll(reader)
    return string(strBytes)
}

I've found a better package, which uses iconv. Usage is trivial, it is described in the documentation. For example:

output,_ := iconv.ConvertString("Hello World!", "windows-1252", "utf-8")

Link to the package: https://github.com/djimenez/iconv-go